Electronic circuits, typically incorporated within integrated circuit (IC) devices, determine the function of various electronic systems, ranging from large systems (such as computer server “farms” that enable the wide variety of Internet services and businesses, and can include hundreds or even thousands of server computers), to the small portable electronic devices such as cellular telephones.
Electronic circuits typically include transistors interconnected to one another to a same integrated circuit substrate and/or package. An integrated circuit (IC) substrate may be a single semiconductor substrate (e.g., die created by dividing a fabricated “wafer”) that includes circuit elements of the electronic circuit. An integrated circuit package may present a set of external connections, but include one or more ICs substrates and circuit components having conductive interconnections to one another.
Digital electronic circuits (hereinafter digital circuits) may form all or a portion of a large majority of circuits included within ICs. Digital circuits may receive and output digital values, typically binary values that vary between low and high logic levels.
Continuing goals for circuits (including digital circuits) include reductions in power consumption, improvements in performance, and reductions in area occupied by the circuit. Because ICs may employ vast numbers (up to millions) of digital circuits, even incremental reductions in power consumption may translate into significant power savings of devices or systems employing such circuits. In the case of large systems, reductions in power consumption can reduce power costs of an enterprise. In the case of portable electronic devices, reductions in power consumption can advantageously lead to longer battery life and/or the ability to provide additional functions for a given amount of charge.
Performance may include various aspects of circuit operation, including but not limited to: the speed at which data values transmitted and/or accessed by digital circuits. Improvements in signal propagation time (e.g., speed) may enable a device to increase the speed at which data is transmitted between locations of a device, thus reducing the time for the device to execute operations. In devices where data is stored, the speed at which data is written and/or read from storage locations may likewise improve device performance. Performance may also include circuit stability. Stability may be the ability of a circuit to provide a sufficient response under particular operating conditions.
Reductions in circuit size may directly translate into cost savings. In the case of ICs, reductions in size may allow more devices to fit on a fabrication substrate: As understood from above, digital circuits may occupy substantially all of the substrate area for some devices, and significant amount of are for others.
As device fabrication technologies approach limits to scaling (i.e., the ability to reduce circuit element sizes) the ability to further advance any of the goals noted above has grown increasingly costly or technically challenging.